Early Embrylogical Development

Question 1

Explain what happens prefertilization/during development with primordial germ cells

Answer 1

During early embryo development the primordial germ cells leavethe vicinity from the yolk sac to the gonodal ridges (location of primary sex cords) and return at week 5

Promordial cells also undergo gametogenesis— involving mieosis and reduce the chromosomes to 23, redistributes chromosol material to ensure genetic varibility and exchanges a small amount of maternal and paterial DNA via crossover

Question 2

Explain what is happening paternal prefertizaltio and in development. What process are male gametes produced through?

Answer 2

Male gametes (spermatocytes) are produced through spermatogensis. Primordial cells Travel from yolk sac to primitive testis duringw eek 4 and are dormant until puberty.

Question 3

What happens at puberty to males

Answer 3

Two types of spermatogonia develop.

Type A- Undergo mitosis to make more Type A and Type B

Type B- that enter Meiossi to from a primary spermatocytes (still 46). —-complete meosis I—> secondary spermatocytes (23)—Meosis ii—-> 4 spermtids—spermiogensis—>sperm

Question 4

When sperm is ejaculated what needs to happen before fertilization? Where? How Long?

Answer 4

Capacitation in the female reproductive tract.

The sperm cycle is about 64 days.

Question 5

What is happening on the female side of things prefertilizatoin?

Answer 5

All female gametes (oocytes) are derived from primary oocytes in the ovaries.

They have 46 chromosomes from the 5th fetal month until puberty and are at meosis I.

Each cycle one egg completes meiosis I and becomes a secondary oocyte (23)— meiosis II—> the sendary stays at metaphase II is surronded by corona radiata and zona pellcuida unless fertilized

If fertilized eggs complete meosis II and become mature oocyte

Question 6

3 important results of fertilization

Answer 6

1. Restoration of diploid chromosomes numbers
2. Determination of choromosomal sex
3. Intiaition of cleavage

Question 7

What must a spermatozoa(oon) do to allow for fertilization?

What 3 things happen immediatley after fertilization?

Answer 7

Penetrate all 3 layers of the oocyte. Corona radiata, zona pellucida and oocyte Cell membrane.

When this pentration happens the 1. egg finished its Meissis II and forms the pronuclues

2. Zona pellucida now impermeable to all other spermatozoa.
3. Head of sperm seperats from the tail, swells and form males pronucleus

Question 8

Where does fertilization normally occur

Answer 8

Ampulla of the uterine tube

Question 9

3 layers of the uterine body

Answer 9

Inner- endometerium- sheds and regenerates

Middle- myometerium- muscular contracts as needed in delivery

Outter= perimetrium

Question 10

Explain the steps following fertlizaton

Answer 10

Miotic Cell division/cleavage in the uterine tube and prepartion for implanation.

1. 2 cell stage=blastomeres
2. 4 cell stage= blastomeres
3. Morula- 16 cell stage (3-4th day after ferilization)= blastocyst– this point it has divided but we are concerned about lack of nutrients or crushing each other
4. Morula- blastocyst- makes an inner cell mass (embryo) and outer cell mass (trophoblast) with opening in center (blastocele)

Question 11

The trophoblast does what?

Answer 11

Divdies into two layers

1. Cytotrophoblast- with distinct cel boundaries and undergoes mitoic division to make syncytiotrophblast
2. Synctiotrophoblast- looks like a blob with blurred lines will grow into the endometerium to make connectio with endometrial blood vessels and makes hCG.

Question 12

When is hCG detectable

Answer 12

8- blood

10 days- urine

Question 13

What the 4 week of 2s.

Answer 13

1. Trophoblast has two layers- cytotrophoblast and syncytiotrophoblast(outer)
2. Embryoblast (from inner cell mass) has two layers- epiblast and hypoblast
3. The extraembroynoc mesoderm spilts into 2 layers- the somatopleure and splanchonopleure
4. Two cavities form- yolk sac(inside the blastocele) and amniotic (inside the inner cell mass)

Question 14

What is happening during implanation? When? Where?

Answer 14

The blastocyst uses the trophoblast to implant into the uterine cavity normally on the superio wall either anterior or posterior.

Normally during wekk 2

Question 15

What is ectopic pregnancy? And what are possible sites (3)?

What usually happens in ectopic pregnancy?

Answer 15

Implantation of the blastocyst outside of the uterine cavity

1. . Uterine Tube
2. Abdoinal cavity
3. Peritoneal covering of intestinal tract.

The embryo dies in the 2nd moth of gestation.

Question 16

What is gastrulation? Where does it begin

Answer 16

Development of 3 basic embroyonic layers (endoderm, ectoderm, mesoderm)

It begins with formation of the primitive streak on the dorsal surface of the epiblast.

Question 17

Explain how the primitive streak look sin early gastrulation

Answer 17

Like a visible groove with slight bulging on either side. It has a primitive groove, primitive node, and primtive pit(on the cephalic end of the streak)

Question 18

Explain how the 3 embryoni layers form

Answer 18

Cells from the epiblast migrate to the primitive streak

1. Some slip underneath it through invagination- endorderm (inner layer)
2. Some slip between the endoderm and the epiblast mesoderm (middle layer)

3 Remaing cells form ectoderm (outer layer)

This makes a trilmainar embroynic disc- something all adults cells can be traced back to.

Question 19

Explain where the notochord extends from? And what is plays a role in? Does it persist in adults? If so where

Where does it lie?

Answer 19

Notochord extends from the primitive node to the oropharyngeal membrane and plays a role in organ formation.

It persist in adults in the interverterbral disc as the nucleus puplous.

It’s formation happens during mesoderm formation and is between the ecotoderm and endorerm and is the first indicaiton of the axial skeleton.

Question 20

What does gastrulation result in

Answer 20

3 important orientations

Cranial: Sacral

Right and Left

Dorsal and Venterl

Question 21

What does folding of the embroyo involve and what does it accomplish?

Answer 21

1. Embroyonic disc starts as flat rounder structure
2. Grows i the cephlocaudal direction
3. This grwoth results in folding of the cranial and caudal end resulting in head and tail folds
4. Heart orginates out of the cranial position and swings down into what is the future thorax
5. Leaving gastrulation to occuring in the caudal folds

Question 22

What other folding happens after head/tail folding

Answer 22

Lateral folding completes formation of adult form. THen ventral folding closing body cavities.

It’s still connected to the yolk sac butit’s eventually pinched off. A cavity forms around the endoderm and is lined with somatic mesoderm and is the parietal layers of serous membrance

Question 23

What develops formr hte splanchic mesoderm

Answer 23

Cardiac and smooth muscle

Question 24

Explain what happens in the development of the Nervous system

Answer 24

1. Notochord induces ectoderm to thinkening making the NEURAL PLATE– central cells of the plate make the neuroectoderm.
2. Lateral edges migrate towards each other to make the primitive spinal cord.
3. At this time neural crest cells from the edge of neuroectoderm and these cells migrate to through embryo to make adult structures

This is neuraltion

Question 25

What are the precurosor to Nervous system and mesdorm structures

Answer 25

Neural plate and Somites

Question 26

What do the neural crest cells form?

Answer 26

Nervous system0 shwaan cells, PNS myelinates cell, dorsal roota ganglia, some cranial ganaglia, autonomic ganlia, gut intrinsic myenteric plexys, submucosal plexus, part of memngines suronding CNS

2. Head and Neck- head mesenchume, forming facial bones, muscle ligament, odontoblast and the dentin producing teeth
3. Skin- pigment prodcuing melanocytes

Question 27

Locaiton of the neural tube

Answer 27

Orginailly in the dorsal midline of the neural tube but after mitosis exit the neuprepithium and then migrate to their adult locations in the body (nervous system, head and neck and skin)

Question 28

What is DiGeorge Syndrome? What’s missing? Features? Why doe it happen

Answer 28

Deleteion in #22

Subtle cranifacial anomilies and cardiovascular anomilies. Sometimes thymic and paratyroid aplasia

Results from ABNORMAL migration and difference of head and neck neural crest

Question 29

What happens in neural tube defects? Causes? SEverity?

Answer 29

Common kind of congential birth defect aht can be genetic or environmental

Typically caused by failure of neural tube closure and/or induction of bony neural arches of spinal cord
• Range in severity from asymptomatic spina bifida occulta to devastating and fatal anencephaly

Question 30

What are the 3 layers of the medoderm and what do they defferntiate into

Answer 30

1. Paraxial- somites- verterbral column- muscles of the trunk, skeletoeon (EXCEPT THE SKULL), some tentons/cartilage, bone, muscle and skin of the back
2. Intermediate Mesoderm- urogenital strucutes
3. Lateral mesoderm- parietal and visceral layers that line the intaembroyic cavity and surronds organs, spleen, adrenal cortex, CV and lyphatic system, blood and lypmh ells

Question 31

Which of the 3 mesoderm layers make somites? Explain it’s further diviosn

Answer 31

Paraxial!

Somites first start in the cephalic region and then proceed to develop in the cranialcaudal direction. There are occipital, cervical, thoracic, lumbar, sacral and coccygeal pairs of somiates

Subdivdies in

1. Sclerotome- surrond spinal cord to form verterbral column and alos tendon/cartilages/bone
2. Dermomyotome- further divides into Myotome (segmental muscles) and Dermatome (dermis of the back)

Question 32

Structures of the 3 layers

Answer 32

Ectoderm (outer layer)- organs and structures that maintain contact with the outside world: nervous
system, sensory epithelium of ear, nose, and eye, skin, hair, nails, pituitary, mammary, sweat glands and
enamel of the teeth.

Mesoderm (middle layer) - connective tissues, tendons, cartilage, bone, muscle, some urogenital
structures (not gonads, ducts and accesory ducts), blood cells, adrenal cortex

Endoderm Layer (inner layer) - gastrointestinal tract; epithelial lining of the respiratory tract; parenchyma of the thyroid, parathyroids, liver, and pancreas, stroma of the tonsils and thymus, the epithelial lining of the urinary bladder, urethra and lining of the tympanic cavity and auditory tube.